Risk Factors of Colorectal Cancer

Executive Summary

Risk factors influence the chance of developing cancer among individuals, but individuals with no risk factors also develop cancer. Risk factors concerning tumor growth in colorectal cancer are due to multiple reasons. An individual with an average risk of colorectal cancer has an approximately 5% overall chance of developing colorectal cancer. Around 95% of colorectal cancers are sporadic, evolving genetic changes that develop possibility after the individual’s birth, so there is no risk of passing on these genetic changes to one’s children. Only 5% of colorectal cancers are evolved due to sporadic inheritance. Other significant risk factors for colorectal cancers include age, gender, race, rare inherited conditions, adenomatous polyps or adenomas, family history of colorectal cancer, food or diet, physical inactivity and obesity, and smoking.

Risk Factors Associated with Colorectal Cancer

A risk factor can be anything that influences the development of any cancer. But having a risk factor, or many, does not give certainty of having particular cancer. Some people with no risk factors can also develop colorectal cancer. 

An individual with an average risk of colorectal cancer has around a 5% overall chance of developing colorectal cancer ​1​. Generally, most colorectal cancers (approximately 95%) are considered sporadic, which means the genetic changes develop by chance after the individual’s birth, so there is no risk of passing on these genetic changes to one’s children.

Inherited colorectal cancers are comparatively rare (about 5%) and happen when gene mutations or changes are passed from one generation to the next within a family ​2​. Often, the cause of colorectal cancer is unknown. 

However, the below-mentioned factors may raise a person’s risk of developing colorectal cancer:

  • Age: The risk of colorectal cancer rises as people grow older. Colorectal cancer can occur in teenagers and young adults, but most colorectal cancers occur in people older than 50. For colon cancer, the average age for diagnosis for women is 72, and for men is 68. It is 63 for both women and men with rectal cancer. Older adults diagnosed with colorectal cancer face unique challenges, specifically concerning cancer treatment. 

It is noteworthy that while colorectal cancer is diagnosed most commonly in older adults, the incidence rate for colorectal cancer decreased by about 3.6% per year in adults 55 and older. Meanwhile, the incidence rate rose by 2% per year in adults younger than 55. The increase is mainly due to the increasing number of rectal cancer. About 11% of all colorectal diagnoses are in people under age 50. 

  • Gender: Men have a marginally higher risk of developing colorectal cancer than women.
  • Race: Black people have the highest sporadic, or non-hereditary, colorectal cancer rates in the U.S. Colorectal cancer is the leading cause of cancer-related death in Black people. Black women have more chances of dying from colorectal cancer than any other racial group. Black men are even more likely to die from colorectal cancer than Black women. The reasons for these differences are not clear. The American College of Gastroenterology encourages Black people to begin screening with colonoscopies at age 45 because Black people have more chances of being diagnosed with colorectal cancer at a young age.
  • Rare inherited conditions: Members of families with certain uncommon inherited conditions have a higher risk of colorectal and other types of cancer. These include:
  • Lynch syndrome, known as hereditary nonpolyposis colorectal cancer (HNPCC)
  • Gardner syndrome, a subtype of FAP
  • Attenuated familial adenomatous polyposis (AFAP), which is a subtype of FAP
  • MYH-associated polyposis (MAP)
  • Familial adenomatous polyposis (FAP)
  • Turcot syndrome, a subtype of FAP and Lynch Syndrome
  • Juvenile polyposis syndrome (JPS)
  • Muir-Torre syndrome, a subtype of Lynch Syndrome
  • Peutz-Jeghers syndrome (PJS)
  • Adenomatous polyps or adenomas: Polyps are not cancer, but a few types of polyps called adenomas can develop into colorectal cancer. Polyps can mostly be eradicated using a tool during a colonoscopy, a test in which the doctor looks into the colon with the help of a lighted tube after the patient has been sedated. Polyp removal can help prevent colorectal cancer. People with adenomas have a higher risk of additional polyps and colorectal cancer, and they should regularly have follow-up screening tests.
  • Family history of colorectal cancer: Colorectal cancer may run in the family if first-degree relatives (parents, sisters, brothers, children) or other family members (grandparents, uncles, aunts, nieces, nephews, grandchildren, cousins) have had colorectal cancer . It is specifically true when family members are diagnosed with colorectal cancer before turning 60. If a person has a family history of colorectal cancer, their chances of developing the disease are double. The risk may increase further if close relatives have also developed colorectal cancer or a first-degree relative was diagnosed at a young age. It is essential to talk to your family members about your family’s history of colorectal cancer. If you have a family history of colorectal cancer, speak with a genetic counsellor before genetic testing. Only genetic testing can determine if you have a genetic mutation, and genetic counsellors are trained to describe the benefits and risks of genetic testing.
  • Food/diet – Current research consistently links eating more red meat and processed meat to higher disease risk ​3​. Other dietary factors are also being studied to see if they affect the risk of developing colorectal cancer.
  • Personal history of specific types of cancer – People with a previous personal history of colorectal cancer or a diagnosis of ovarian cancer or uterine cancer are more likely to develop colorectal cancer ​4​.
  • Physical inactivity and obesity: People who live an inactive lifestyle, that is, no regular exercise and more sitting, and people who are overweight or obese may have a higher risk of colorectal cancer.
  • Smoking – Recent studies have shown that smokers are more likely to die from colorectal cancer than nonsmokers.


  1. 1.
    Johnson CM, Wei C, Ensor JE, et al. Meta-analyses of colorectal cancer risk factors. Cancer Causes Control. Published online April 6, 2013:1207-1222. doi:10.1007/s10552-013-0201-5
  2. 2.
    Levin B, Lieberman DA, McFarland B, et al. Screening and Surveillance for the Early Detection of Colorectal Cancer and Adenomatous Polyps, 2008: A Joint Guideline from the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. CA: A Cancer Journal for Clinicians. Published online May 1, 2008:130-160. doi:10.3322/ca.2007.0018
  3. 3.
    Willett WC. Diet and Cancer. JAMA. Published online January 12, 2005. doi:10.1001/jama.293.2.233
  4. 4.
    CANAVAN C, ABRAMS KR, MAYBERRY J. Meta-analysis: colorectal and small bowel cancer risk in patients with Crohn’s disease. Aliment Pharmacol Ther. Published online April 2006:1097-1104. doi:10.1111/j.1365-2036.2006.02854.x